Multilayers having reduced perpendicular demagnetizing field using moment dilution for spintronic applications

Abstract

A magnetic element is disclosed that has a composite free layer with a FM1 / moment diluting / FM2 configuration wherein FM1 and FM2 are magnetic layers made of one or more of Co, Fe, Ni, and B and the moment diluting layer is used to reduce the perpendicular demagnetizing field. As a result, lower resistance x area product and higher thermal stability are realized when perpendicular surface anisotropy dominates shape anisotropy to give a magnetization perpendicular to the planes of the FM1, FM2 layers. The moment diluting layer may be a non-magnetic metal like Ta or a CoFe alloy with a doped non-magnetic metal. A perpendicular Hk enhancing layer interfaces with the FM2 layer and may be an oxide to increase the perpendicular anisotropy field in the FM2 layer. The magnetic element may be part of a spintronic device or serve as a propagation medium in a domain wall motion device.

Description

RELATED PATENT APPLICATIONS[0001]This application is related to the following: Docket #HMG10-023, Ser. No. 12 / 927,939, filing date Nov. 30, 2010; and Docket #HMG10-038, Ser. No. 12 / 931,866, filing date Feb. 11, 2011, assigned to a common assignee and herein incorporated by reference in their entirety.FIELD OF THE INVENTION[0002]The invention relates to a composite magnetic structure having a layer that reduces saturation magnetization Ms in order to lower the perpendicular demagnetizing field thereby enhancing the perpendicular anisotropy field to lower the resistance-area (RA) product, and increase thermal stability independently of the moment, volume, or crystalline anisotropy for a device with perpendicular to plane magnetization.BACKGROUND OF THE INVENTION[0003]Magnetoresistive Random Access Memory (MRAM), based on the integration of silicon CMOS with magnetic tunnel junction (MTJ) technology, is a major emerging technology that is highly competitive with existing semiconductor ...

AI Technical Summary

Benefits of technology

[0022]The objective of the present invention is to provide a magnetic element with a composite free layer having out-of-plane magnetization in which saturation magnetization is reduced to improve thermal stability independently of the moment, volume, or crystalline anisotropy while maintaining a high MR ratio.

[0023]According to one embodiment, these objectives are achieved by providing a magnetic tunnel junction (MTJ) comprised of a pinned layer, a tunnel barrier layer, and a magnetic element including a composite free layer having a Ms reducing (moment diluting) layer formed between two magnetic layers (FM1 and FM2). The FM1 layer has a surface that forms a first interface with the tunnel barrier while the FM2 layer has a surface facing away from the tunnel barrier that forms a second interface with a perpendicular Hk enhancing layer which is employed to increase the perpendicular anisotropy field within the FM2 layer. There is a capping layer as the uppermost layer in the MTJ stack. In an embodiment wherein the perpendicular Hk enhancing layer is an oxide such as MgO, the capping layer is preferably a metal with an energy of oxide formation considerably greater than that of the perpendicular Hk enhancing layer. Thus, the MTJ has a bottom spin valve configuration that may be represented by seed layer / AFM layer / pinned layer / tunnel barrier / composite free layer / perpendicular Hk enhancing layer / capping layer. Both of the first and second interfaces provide strong perpendicular surface anisotropy for FM1 and FM2 layers, respectively.

Problems solved by technology

As the size of MRAM cells decreases, the use of external magnetic fields generated by current carrying lines to switch the magnetic moment direction of the free layer becomes problematic.

This high current density, which is required to induce the spin-transfer effect, could destroy a thin tunnel barrier made of AlOx, MgO, or the like.

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